Method of plating articles having small clearances or crevices

ABSTRACT

A method for plating articles, particularly chains, having small clearances or crevices formed by closely spaced article surfaces to be plated. A plating solution is applied to the article, the level of the pressure acting on the plating solution is reduced, and the plating solution is heated and boiled. The plating solution soaks up into the clearances to plate metal onto article surfaces that could not be plated by using conventional methods.

United States Patent Avramidis et al.

1451 July 15, 1975 [54] METHOD OF PLATING ARTICLES HAVING 2,865,375 12/1958 Banks et al ll7/l30 E X SMALL CLEARANCES 0R CREVICES 3,158,500 1 H1964 $3110 at al. 117/130 E X 3,755,890 9/1973 Klehm, Jr. 117/61 1 [75] Inventors: Stellios A. Avramidis, Greenfield; 1 Ivan Rhoden Plainfield both of Primarv Examiner-Leon D. Rosdol Assistant ExaminerJohn D. Smith [73] Assignee: FMC Corporation, San Jose, Calif. f g n Vefhovefl; E. 221 Filed: Dec. 3, 1973 211 Appl. No.: 420,816 [57] ABSTRACT A method for plating articles, particularly chains, hav [52] 11.8. C1. 427/295 i all l aran es or revices formed by closely 1 '1 q B3219 C spaced article surfaces to be plated. A plating solution 1 Field 1 2 1 130 1 130 R is applied to the article, the level of the pressure acting on the plating solution is reduced, and the plating 1 1 References Cited solution is heated and boiled. The plating solution UNITED STATES PATENTS soaks up into the clearances to plate metal onto article 2,465,747 3/1949 'Pessel 204/278 sPrfaces that could be Plated by using Conven- 2,s30,9s4 11/1950 ll7/6l x tlonal methods- 2,554,254 5/1951 Kroft 1 1 1 1 1 17/61 2,576,3[9 11 1951 Toulmin, Jr. et al. 117/169 A 4 Clams 3 Draw F'guns CONTROL 40b VALVE a 34 I 40 1 G 32 l I 1a VACUUM l 6b n '32 1::

- COOLING COIL as SCREEN BASKET 3 G2.

PLATING PLATING SOLUT'ON TANK 16* SHEET i uUHIW-P n CONTROL 40b VALVE a 6D 34 l 40 j" G 2 L l VACUUM 38b N N 1 2:, 244 16b i 32b COOLING con. 2 e s SCREEN 7 BASKET G2.

PLATING PLATING ammo: TANK 16"" CHAiN so I 65 ea 620.. a 64- G6 2 METHOD OF PLATING ARTICLES HAVING SMALL CLEARANCES OR CREVICES BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method for plating chains or other articles having small clearances or crevices that are to be penetrated by plating solution.

2. Description of the Prior Art Plating metal may be accomplished by electroplating (that is, electrolytically) or by electroless plating. Conventional plating, or electroplating, is accomplished when metal ions are reduced to metal and deposited as such at the cathode by the use of electricity. Electroless plating (a typical example of which is described in US. Pat. No. 2,532,283) is accomplished by chemical reduction of the metallic ion in an aqueous solution and the subsequent deposition of metal without the use of applied electricity.

The plating of articles, by electrolytic or electroless means, sometimes is accomplished by using special techniques. One technique which is of interest, disclosed in U.S. Pat. No. 2,465,747 to L. Pessel, involves evacuating gas, or air, from a plating tank chamber containing a heated electrolytic plating solution in which an article to be coated, by electrodeposition of metal, is immersed. Certain benefits are obtained by evacuating the space in the plating tank above the electrolytic plating solution. One benefit is that gas bubbles adhered to the immersed article quickly separate from the article and stir the electrolyte. Separation of the gas bubbles from the surface of electrodeposited metal allows for further deposition of electrodeposited metal.

Chains plated with corrosion resistant metal have been produced by using either electrolytic or electroless metal deposition techniques involving immersion of the chains into either an electrolytic or electroless plating solution subjected to atmospheric pressure in an open-to-the-atmosphere plating tank. The electroless process tends to produce a more uniform coating of metal than the electrolytic process. Mechanical stirrers have been used to stir or agitate the plating solution to facilitate the desired plating action.

It has been found that electroless nickel plated chains, which are to be used in corrosive environments, having small clearances or crevices are not entirely satisfactory. They characteristically include certain surface areas that should be plated but do not receive a coating of plated metal during the plating process. Undesirable rust spots can quickly develop at these unplated surfaces of the chain. The unplated surfaces are found at the chain joints where parts or surfaces of the chain are closely spaced to form small clearances or crevices. These clearances or crevices entrap or retain gas particles or bubbles so that the liquid of the plating solution is unable to penetrate into the clearances. The gas particles or bubbles shield the nearby chain surfaces from wetting contact with the plating solution liq uid, keep the liquid from soaking, or penetrating, into the aforesaid clearances, and thereby prevent plating of metal onto gas shielded or occluded surfaces of the chain thus rendered inaccessible to wetting contact with the liquid. A definite need exists for a plating tech nique which can be used to plate chains or other articles having small clearances or crevices associated with article surfaces to be plated but normally inaccessible to wetting contact with the plating solution.

SUMMARY OF THE INVENTION This invention provides a method especially adapted for use in the electroless plating of chains or other articles having small clearances or crevices that must be penetrated by plating solution to effect the electroless plating of relatively inaccessible article surfaces. The method includes the step of reducing the level of the pressure acting on the electroless plating solution to allow the plating solution liquid to penetrate or soak into the clearances of the chain or similar article. In one form of the invention, incipient boiling of the solution is provided to help the agitation of the solution. Gas, namely air, is evacuated from the plating tank chamber in which the chain or similar article is immersed so that a good electroless plating action is obtained on the closely spaced chain surfaces.

The accompanying drawings will be used in describing the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic perspective representation of an apparatus suited for use in carrying out the method of the present invention. Some parts of the apparatus are shown partially cutaway for illustrative purposes.

FIG. 2 is a section of the plating tank taken along lines 2-2 of FIG. 1.

FIG. 3 is an enlarged illustration of an article, namely a chain, which is plated by use of the method of the present invention. Some of the parts of the chain are shown in cross-sectionv DESCRIPTION OF THE PREFERRED EMBODIMENT A particular electroless plating apparatus 10 suited for use in performing the method of the invention is illustrated in the drawings. The illustrated apparatus 10 includes a receptacle tank 12 containing heated water 14 and a plating tank 16 resting on the bottom of tank 12. The plating tank I6 includes a stainless steel container I6a provided with a gasket G (FIG. 2) at its top end and includes a stainless steel cover 16b placed on the upper end of the container to define a tank chamber. The insides of the container and cover are lined with a suitable inert material such as tetrafluoroethylene 17.

Tank 16 contains an electroless nickel plating solution 18, or other suitable metal plating solution, which plates metal by chemical reduction onto a metal chain 60, or other article, submerged in the solution. The apparatus includes a heating means 20 for heating the water 14 which heats the plating tank 16 which in turn heats the plating solution [8. Electrically conductive heater elements 20, constituting the heater means which are embedded in the bottom wall of the tank 12, are heated by passing electrical current through them to heat the bottom wall of the tank 12 and the water 14. The tank 12 is made entirely of thermally conductive, electrically nonconductive, ceramic material and the heater elements are electrically insulated wires but any suitable construction may be used.

The apparatus [0 includes a vacuum pump 22 driven by a motor M connected to the plating tank I6 by a vacuum line. indicated generally by numeral 24 and comprised of several sections of tubing. The pump acts to pump gas, namely air, out of the chamber of the plating tank I6. Line 24 includes a rubber tubing section 24a connecting the vacuum pump to a cold trap unit 26, a rubber section of tubing 24b connecting cold trap unit 26 to another cold trap unit 28, a section of rubber tubing 24c connecting cold trap unit 28 to a cooling coil unit 30, and a section of rubber tubing 24d connecting cooling coil unit 30 to the plating tank cham ber.

The cold trap unit 26 includes an open top container 260 containing cold tapwater 26b and a glass flask 26(- having a removable rubber stopper 26d closing its open upper end. Two glass tubes 26c and 26fproject through the stopper 26d and their upper ends fit into respective ends oi the tubing sections 24a and 2417. (old trap unit 28, generally similar to unit 26, includes an open top container 2811 containing cold tapwater 28b and a glass flask 28( having an integral glass tubing 28d and a re movable rubber stopper 28: closing the upper end of the flask 281'. A glass tubing 28fprojccts through the stopper 28c. Respective ends of the sections of tubing 24c and 24b lit onto the sections of tubing 28d and 28f.

Cooling coil unit 30 includes an open top container 30:: containing cold tapwater 30b and a tubular cooling coil 30c, made ol copper or other metal. The coil 30c has two ends that connect with nearby ends of tubing sections 24c and 24d. One end of the tubing section 2411 connects with one end of a horizontal tube 32a of a tee fixture 32 mounted on the plating tank cover 1611. The horizontal tube portion 32a intersects with a vertical tube portion 32b of the fixture The lower end of tubing 32!) projects laterally through the cover 16b into the Q plating tank chamber. A vacuum, or pressure, gauge 34 on the upper end of the tube 32b provides pressure gauge readings, in inches of mercury, to indicate the pressure level in the plating tank chamber. A control valve 36 on one end of tube portion 32a has an opening 361; to atmosphere and a control handle for manual adjustment of the pressure level in the plating tank chamher.

A tank cooling coil 38, made of copper tubing, affixed to the cover includes end portions projecting through the cover with coil ends 38a and 38b located outside of the plating tank. Rubber tubing sections 40a and 40b connect with respective cooling coil ends 380 and 38b. Tubing 40a connects with a water faucet (not shown) and tubing 38a drains into a wash basin (not shown) or the like, Cold tapwater flows from the water faucet through the tubing 40a, the tank cooling coil 38, and the tubing 40b to cool the cooling coil so that evaporated water from the plating solution condenses on the turns of the coil 38, liquefies, and falls into the plat ing solution. This condensation action helps to keep the plating solution composition (ie, chemical makeup) relatively constant and limits water loss from the plat ing solution during the plating action.

The cold trap units 26 and 28 and the cooling coil unit 30 limit the amount of water that can reach the vacuum pump 22 from the plating tank chamber. These units protect the vacuum pump 22 from being rendered inoperative. during a plating process, by water vapor evolving from the plating solution 18, traveling through line 24, and condensing in the vacuum pump, Evaporated water from the plating solution is cooled as it flows through the units and the line 24 toward the vacuum pump. Evaporated water passing through the cool ing coil 300 is cooled down by contact with the coil and condenses into liquid 1.. which collects in the flasks of the units 26 and 28.

Any suitable electrolcss nickel plating solution 18 is used. One such solution is formulated by mixing a commercially available liquid preparation, such as NIK- LAD 792A (available from the Allied-Kelite Products Division of the Richardson Company, 2400 East Devon Avenue, Desplaincs, Illinois) with Sodium Hypophosphate and water. Specifically, the plating solution is prepared in a conventional manner by mixing 7.5 gallons of NIKLAD 792A, 4.7 pounds of Sodium Hypophosphatc, and 225 gallons of water. The plating tank 16 is filled about three-quarters full with the solution.

To plate an article, the cover 16b is lifted from the container 16a and the article to be plated is submerged in the plating solution in the plating tank. In this instance, the article is a 10 foot long strand of roller chain including small or interstices clearances (e.g., .003 to .0005 inch) in chain joints of the chain. The chain 60 is submerged in the plating solution 18 in suitable fashion. Thus, for example, the strand of chain 60 is wound into a coil and placed into a mesh or net formed into a screen basket 62 open at one end. The basket 62 is made of nylon or other suitable material. The coiled chain 60 in the basket 62 is lowered into the plating solution. The open end of the basket 62 is stretched over the top end of the container and held in place as the cover 1611 is replaced onto the open upper end of the container 16a. The cover and container hold the basket 62 in place with the coiled chain 60 resting on the basket below the surface of the plating solution 18. Hooks (not shown) may be attached to the cover or container and used to hold the basket in place.

The procedure for plating the chain 60 is started by electrically energizing the heater elements 20 to heat the water 14, tank 16, and the solution 18 to raise the temperature of the solution 18 to a suitable temperature, say F. The vacuum pump is started up and evacuates gas, namely air, from the plating tank chamber. As gas, or air, is pumped out of the chamber, the pressure level in the chamber decreases to a suitable subatmospheric pressure level established by adjusting the control valve 36 (which has a variable size opening) to vent air from the atmosphere to the vacuum pump and to the plating tank chamber. Thus, a partial vacuum is established inside the plating tank or chamber above the upper surface ot" the plating solution.

The temperature oi" the plating solution 18 and the pressure level in the plating tank chamber are regulated to establish a desired condition in the plating tank chamber so that as the plating action proceeds, the solution will ultimately reach an incipient boiling condition. Incipient boiling helps the agitation of the solution, but vigorous boiling is more harmful than beneficial because of the resulting evaporation. The boiling point temperature of the plating solution drops with decreasing pressure level in the plating tank chamber, but. in any event, the plating solution is heated to a temperature in excess of 160F., which is approximately the lowest temperature at which a plating action can be attained, and to a temperature to make the solution begin to boil. The incipient boiling action agitates or stirs the solution liquid to help prevent localized temporary exhaustion of the plating agent of the solution, and aids in obtaining relatively complete plating of inaccessible chain surfaces, by causing agitation or circulation of the solution liquid near such surfaces.

The subatmospheric pressure level, or partial vacuum, established in the plating tank chamber causes particles or bubbles of gas, or air, entrapped between closely spaced parts or surfaces of the chain 60 to migrate out of the clearances between such parts and surfaces to allow the plating solution to penetrate, or soak, into the clearances into wetting contact with respective chain surfaces that would otherwise not be contacted by the plating solution liquid because of the surface tension of the liquid.

A typical plating procedure carried out in the described manner involves keeping the plating solution temperature at about 195F. and keeping the plating tank chamber pressure at about inches of mercury for an interval of about 45 to 60 minutes to build up an electroless nickel plating of about .0005 to .OOIO inches on exposed chain surfaces and a somewhat thinner but sufficiently thick plating on the relatively inaccessible chain surfaces. In carrying out the process the chamber pressure may be set to be anywhere from about l0-27 inches of mercury while heating the plating solution to a temperature in a fairly wide temperature range. The temperature can be as low as about 160F. After the desired thickness of nickel has been plated onto the chain, the chamber pressure is returned to atmospheric pressure and the plated chain is removed from the plating tank.

A portion of a strand of chain 60 is shown in FIG. 3 to show parts of the chain that are coated with nickel by using the aforedescribed method. The chain includes link side bars 62 and 64 and bushings 66, rivet pins 68, and rollers 70 at the chain joints. Plated metal is deposited at the chain joints (where adjacent side plates overlap) on closely spaced side bar surfaces 62a, 640; on the inside bushing surface 66a; and on the rivet pin surface 680 inside the bushing; and on the other surfaces of the chain. The clearance between side bars 62 and 64 is typically .005 inch or more and the clearance between bushing surface 660 and the rivet pin surfaces 68a is typically .003 to .005 inch or more. These clearances are so small that past attempts, using prior art methods, to electroless plate the surfaces 62a, 64a,

66a and 68a have been unsuccessful. The method of the invention produces chains in which these surfaces are plated to a satisfactory degree.

Although the best mode contemplated for carrying out the present invention has been herein shown and described, it will be apparent that modification and variation may be made without departing from what is regarded to be the subject matter of the invention.

What is claimed is:

l. A method of plating a chain including joints that have crevices to be plated with metal and simultaneously removing trapped gas from the crevices of the chain to enable the surfaces to be plated; said method comprising the steps of:

submerging the chain in an electroless plating solution contained in the chamber of a plating tank when the gas pressure in the tank above the solution is at atmospheric level;

heating the plating solution and evacuating gas from the plating tank chamber to establish a condition in which the plating solution reaches an incipient boil under subatmospheric pressure, whereby the pressure of gas trapped within the crevices of the chain is increased relatively above the adjacent liquid pressure and the solution liquid frees gas from entrapment in crevices at the chain joints so that the solution penetrates into the crevices to plate metal onto surfaces of the chain that could not be plated but for the freeing of the entrapped gas.

2. The method set forth in claim 1 wherein the crevices are spaced by a distance as small as fivethousandths of an inch.

3. The method set forth in claim 1 wherein the gas pressure in the tank above the electroless plating solution is reduced to at least 10 inches of mercury.

4. The method set forth in claim 3 wherein the plating solution is heated to a temperature only sufficient to maintain an incipient boiling condition.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. n 3,895, 137

DATED July 15, 1975 v INVENTORG) STELLIOS-A. AVRAMIDIS et al It is certified that error appears in the ah0ve-identified patent arid that said Letters Patent are hereby corrected as shown below;

In th e'Abstract, in line 8, delete "up".

Col. 4, line 1.6, after "small" insert clearances;

.' same line, after "interstices" delete "clearances";

Signed and Scaled this A ttesr:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner oj'Parenrs and Trademarks 

1. A METHOD OF PLATING A CHAIN INCLUDING JOINTS THAT HAVE CREVICES TO BE PLATED WITH METAL AND SIMULTANEOUSLY REMOVING TRAPPED GAS FROM THE CREVICES OF THE CHAIN TO ENABLE THE SURFACES TO BE PLATED, SAID METHOD COMPRISING THE STEPS OF: SUBMERGING THE CHAIN IN AN ELECTROLESS PLATING SOLUTION CONTAINED IN THE CHAMBER OF A PLATING TANK WHEN THE GAS PRESSURE IN THE TANK ABOVE THE SOLUTION IS AT ATMOSPHERIC LEVEL, HEATING THE PLATING SOLUTION AND EVACUATING GAS FROM THE PLATING TANK CHAMBER TO ESTABLISH A CONDITION IN WHICH THE PLATING SOLUTION REACHES AN INCIPIENT BOIL UNDER SUBATMOSPHERIC PRESSURE, WHEREBY THE PRESSURE OF GAS TRAPPED WITHIN THE CREVICES OF THE CHAIN IS INCREASED RELATIVELY ABOVE THE ADJACENT LIQUID PRESSURE AND THE SOLUTION LIQUID FREES GAS FROM ENTRAPMENT IN CREVICES AT THE CHAIN JOINTS
 2. The method set forth in claim 1 wherein the crevices are spaced by a distance as small as five-thousandths of an inch.
 3. The method set forth in claim 1 wherein the gas pressure in the tank above the electroless plating solution is reduced to at least 10 inches of mercury.
 4. The method set forth in claim 3 wherein the plating solution is heated to a temperature only sufficient to maintain an incipient boiling condition. 